WASHINGTON - The Supreme Court said Monday that it would hear two major appeals from corporate America that seek to block mass lawsuits before they reach trial.

Many other pending class-action suits will slow or stop while litigants and courts await the decision in these two cases.

One case involves a huge sex-bias claim against Wal-Mart Stores Inc., and the other is a massive environmental suit that seeks to hold coal-fired power plants liable for causing global warming.

Monday's move is the latest sign that the Supreme Court under Chief Justice John Roberts is inclined to rein in big-money lawsuits against business. The conservative justices have been particularly skeptical of sprawling suits that could run on for years and lead to huge verdicts.

In the "global warming" case, electricity industry lawyers played up this theme. They cited the mass litigation over asbestos and tobacco and said the climate-change suits, unless halted, could make those "look like peanuts."

In the Wal-Mart employment discrimination case, the justices will decide whether the retail giant can be sued for sex bias in the largest workplace class action in the nation's history. A federal judge and the U.S. court of appeals in San Francisco cleared the suit to proceed as a class action on behalf of as many as 1.5 million women who were employed at Wal-Mart in the past decade. The suit contends that women were regularly paid less than men and denied promotions.

The justices will not decide whether Wal-Mart is guilty of sex bias. Instead, they will rule on whether it must defend itself against a single lawsuit that speaks for more than a million employees.

Since 1966, the federal rules of civil procedures have allowed individual plaintiffs to sue as "representative" of a class of persons, but "only if there are questions of law or fact common to the class."

The lawyers who sued Wal-Mart said the company has a common corporate culture that reserves most management jobs for men. Wal-Mart disagrees and argues that because hiring and promotions decisions are made by individual managers in its 3,400 stores, the employees do not have enough in common to make class-action treatment appropriate.

The issue of when any suit can proceed as a class action is of great interest to corporate lawyers and the trial bar. If a suit gets the go-ahead to proceed as a class action, companies feel pressure to offer a settlement rather than risk a potentially crippling jury verdict.

The "global warming" suit, if allowed to proceed, could be even more significant. It will decide whether judges can rule that pollution is a public nuisance and on that basis set limits on carbon emissions.

The case to be heard by the court concerns power plants in the Midwest, but similar "nuisance" suits have been filed against the auto, oil, coal and chemical industries, asserting they should be held liable for contributing to climate change.